Pungency principle in chilli is

The pungency principle in chilli is Capsaicin.
The spiciness in chili peppers is known as pungency and it is due to the presence of a group of compounds called capsaicinoids. Capsaicin is the major spice-producing alkaloid present in peppers.
It is a mixture of closely related compounds called capsinoids. Chief among these is the compound capsaicin, which is known by the chemical name: (E)-N-[(4-hydroxy-3-methoxyphenyl) methyl]-8-methyl-6-nonenamide.